Can anything with mass be entangled and if so does this show gravity is of a quantum nature? I read an article ( "Synopsis : A Test of Gravity's Quantum Side.") I read on physics.org  where "mass" was being considered in an entanglement experiment by two scientists and the article said an interferometer would be used in the entanglement process.  
I think I recall in physics class photons are massless?  so I was wondering how a mass could be used in an interferometer and if it could then would that  mean that gravity was quantum by default?  Just puzzled by the article. Thank you.  
 A: Firstly, you can use any massed particles, e.g. electrons, for interferometer experiments. Interference is only about quantum nature of a particle, and it directly shows you the uncertainty relation about the particle's position and momentum. 
Secondly, I guess what's in your mind is: since gravity is directly related to mass distribution in the space-time, while mass itself is an intrinsic property of a particle (bare one or renormalized one not bothering here), hence mass distribution can be directly related to position of particles; then that means the space-time structured affected by mass distribution would be related to the position of particles, which has a quantum effect.
Well, a super un-responsible answer is "Yes" -- just for fun, you could even naively view this as the simplest reason for requiring the quantization of gravity, which is what people are trying to do right now. 
But, apparently, if you literally just start from the mass distribution using uncertainty relation, and then repeat Einstein's general relativity theory, that doesn't directly give you a consistent quantum theory for gravity at all. 
If you use quantum field theory perspective, though, particles are treated as excitations of fields, and therefore you might should forget about particles and so-called "intrinsic property" mass; but, rather, view mass as a parameter in the field theory, which, more essentially, could sometimes be viewed as a resulted phenomena of so-called spontaneous symmetry breaking, or Higgs mechanism.
Your logic that starting from GR to approach quantum theory (which is the opposite direction of string theory) might not be completely wrong, which is the logic of loop quantum gravity theory. However, there the main concern should be, very un-precisely, quantizing space-time structure firstly(using spin network), and the characterizing length of the network is of Planck length scale. In that theory, basically gravity is treated more or less like a gauge theory of Lorentz group. 
You need more basic knowledge to explore further.
